Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, a nacelle rotatably supported on the tower, a generator housed in the nacelle, and one or more rotor blades. The rotor blades capture kinetic energy from wind using known airfoil principles, and transmit the kinetic energy through rotational energy to turn a shaft that couples the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid. With the growing interest in wind generated electricity, considerable efforts have been made to develop wind turbines that are reliable and efficient.
Current wind turbines typically include an overspeed monitoring system that monitors the rotor speed relative to a fixed overspeed setting(s) (i.e., a fixed maximum rotor speed setting(s) for the wind turbine). In general, the fixed overspeed setting(s) is determined as a function of the predetermined, nominal speed for the wind turbine. For example, the fixed overspeed setting(s) may be set as a maximum speed setting that is greater than the wind turbine's nominal speed. In such instance, if the rotor speed for the wind turbine exceeds the fixed overspeed setting(s), a control action may be implemented by the overspeed monitoring system to reduce the rotor speed and/or to shutdown the wind turbine.
In many instances, it is desired to operate a wind turbine at reduced speeds (e.g., at a speed setting below the turbine's nominal speed). For example, a wind turbine may often be operated at a derated speed to compensate for the higher loads caused by higher air densities. Unfortunately, given the configuration of conventional overspeed monitoring systems, the fixed overspeed setting(s) applied by a current monitoring system is the same regardless of whether the speed setpoint for the wind turbine is set at the nominal speed or a reduced speed. Thus, if a failure of the turbine controller occurs while the wind turbine is operating at reduced speeds, the turbine rotor is allowed to accelerate across a large range of speed values from the reduced rotor speed to the fixed overspeed setting(s) prior to any control action being implemented by the overspeed monitoring system. Such significant acceleration of the rotor often results in the load capabilities of one or more of the wind turbine components being exceeded, thereby leading to damage and/or failure of such component(s).
Accordingly, a system and method for improved overspeed monitoring of a wind turbine operating at reduced rotor speeds (e.g., at a speed setpoint below its nominal speed) would be welcomed in the technology.